This invention relates generally to vibration sensing arrangements, and more particularly, to a vibration sensor mounting fixture which is retained in an opening of a turbine housing by a collettype holding device.
Mounting fixtures for holding vibration sensors have been applied to the measurement of the vibration or deflection of a shaft of large rotating machines such as steam turbines. In recent years, the vibration sensors which are most commonly used are of the non-contacting, distance measuring type. Such sensors perform as transducers, and operate on the eddy current principle by producing an electrical signal which corresponds to the distance between the face of the transducer and the surface of the shaft of the machine. Thus, as the distance between the transducer and the machine shaft varies as a result of vibration, a fluctuating electrical vibration signal is generated at the output terminals of the transducer.
U.S. Pat. No. 3,898,562 describes an arrangement for mounting a transducer within a machine housing. The arrangement described therein is provided with a probe tube which is externally threaded at an upper end so as to permit threaded engagement with an internal thread of a base plate which is mounted on the machine housing. The distance between the measuring surface of the sensing unit which is located on the lower end of the probe tube, and the vibrating machine part is accomplished by rotating the probe tube in the mounting plate so that the threaded engagement causes an axial adjustment of the depth of the probe tube into the machine housing. It is apparent, therefore, that the permissible range of travel in the axial direction in this known system is relatively small, thereby requiring a variety of mounting fixtures or probe tubes to be provided for different depths. In addition, the manufacturing processes required to produced the large diameter threads on the exterior of the probe tube and the interior of the mounting plate result in substantial manufacturing costs.
It is, therefore, an object of this invention to provide an improved mounting fixture for a vibration sensor which permits continuous axial adjustment of the depth to which the vibration sensor protrudes into the machine housing, over a range of 25% of the maximum protrusion.
It is a further object of this invention to provide a mounting fixture for a vibration sensor which easily permits the vibration sensor to be placed at a predetermined calibration distance from the vibrating part within the machine which is desired to measured.